1. Field of the Invention
The present invention relates to an ink-jet printhead and a method for manufacturing the same. More particularly, the present invention relates to an ink-jet printhead, in which an ink passage is formed in a same plane as an ink chamber to improve ejection performance, a metallic nozzle plate is disposed on a substrate to improve linearity of ink droplets ejected through a nozzle, and heat generated by a heater is effectively dissipated to increase a driving frequency of the printhead, and a method for manufacturing the same.
2. Description of the Related Art
In general, ink-jet printheads are devices for printing a predetermined image, color or black, by ejecting a small volume droplet of ink at a desired position on a recording sheet. Ink-jet printheads are generally categorized into two types depending on which ink ejection mechanism is used. A first type is a thermal ink-jet printhead, in which a heat source is employed to form and expand a bubble in ink to cause an ink droplet to be ejected due to an expansion force of the formed bubble. A second type is a piezoelectric ink-jet printhead, in which an ink droplet is ejected by a pressure applied to the ink due to a deformation of a piezoelectric element.
An ink droplet ejection mechanism of a thermal ink-jet printhead will now be explained in detail. When a current pulse is supplied to a heater, which includes a heating resistor, the heater generates heat and ink near the heater is instantaneously heated to approximately 300° C., thereby boiling the ink. The boiling of the ink causes bubbles to be generated, expand and exert pressure on the ink filling an ink chamber. As a result, ink around a nozzle is ejected from the ink chamber in droplet form through the nozzle.
A thermal ink-jet printhead is classified into a top-shooting type, a side-shooting type, and a back-shooting type, depending on a growth direction of a bubble and an ejection direction of an ink droplet. In a top-shooting type printhead, a bubble grows in the same direction in which an ink droplet is ejected. In a side-shooting type of printhead, a bubble grows in a direction perpendicular to a direction in which an ink droplet is ejected. In a back-shooting type of printhead, a bubble grows in a direction opposite to a direction in which an ink droplet is ejected.
An ink-jet printhead using the thermal driving method should satisfy the following requirements. First, manufacturing of the ink-jet printheads should be simple, costs should be low, and should facilitate mass production thereof. Second, in order to obtain a high-quality image, cross talk between adjacent nozzles should be suppressed while a distance between adjacent nozzles should be narrow; that is, in order to increase dots per inch (DPI), a plurality of nozzles should be densely positioned. Third, in order to perform a high-speed printing operation, a period in which the ink chamber is refilled with ink after being ejected from the ink chamber should be as short as possible and the cooling of heated ink and heater should be performed quickly to increase a driving frequency.
FIGS. 1 through 3 illustrate various structures of conventional thermal ink-jet printheads using the back-shooting method.
FIG. 1 illustrates a perspective view of a structure of a conventional ink-jet printhead. Referring to FIG. 1, an ink-jet printhead 20 includes a substrate 11, a cover plate 3, and an ink reservoir 12. The substrate 11 has a plurality of nozzles 10 through which ink droplets are ejected and an ink chamber 16 filled with ink to be ejected. The cover plate 3 has a through hole 2 providing flow communication between the ink chamber 16 and the ink reservoir 12, which supplies ink to the ink chamber 16. In addition, a heater 42, having a ring shape, is disposed around the nozzle 10 of the substrate 11.
In the above structure, if a pulse current is applied to the heater 42 and heat is generated by the heater 42, ink in the ink chamber 16 boils and bubbles are generated and continuously expand. Due to this expansion, pressure is applied to ink filling the ink chamber 16. As a result, ink is ejected in droplet form through each of the plurality of nozzles 10. Subsequently, ink flows into the ink chamber 16 from the ink reservoir 12 through the through hole 2 formed in the cover plate 3. Thus, the ink chamber 16 is refilled with ink.
In this first conventional ink-jet printhead 20, however, a depth of the ink chamber 16 is almost the same as a thickness of the substrate 11. Thus, unless a very thin substrate is used, the size of the ink chamber 16 increases. Accordingly, pressure generated by bubbles for ejecting ink is dispersed by the ink, resulting in degradation to an ejection property. When a thin substrate is used to reduce the size of the ink chamber 16, it becomes more difficult to process the substrate 11. By way of example, a depth of the ink chamber 16 in a typical conventional ink-jet printhead is about 10-30 μm. In order to form an ink chamber having this depth, a silicon substrate having a thickness of 10-30 μm should be used. It is virtually impossible, however, to process a silicon substrate having such a thickness using existing semiconductor processes.
Further, in order to manufacture an ink-jet printhead having the above structure, the substrate 11, the cover plate 3, and the ink reservoir 12 are bonded together. Thus, a process of manufacturing such an ink-jet printhead becomes complicated, and an ink passage, which significantly affects an ejection property, cannot be very elaborate.
FIG. 2 illustrates a cross-sectional view of a structure of another conventional ink-jet printhead. Referring to FIG. 2, a hemispherical ink chamber 15 is formed in a substrate 30 formed of silicon. A manifold 26, which supplies ink to the ink chamber 15, is formed under the substrate 30. An ink channel 13, which provides flow communication between the ink chamber 15 and the manifold 26, has a cylindrical shape and is formed perpendicular to a surface of the substrate 30. A nozzle plate 20, having a nozzle 21 through which ink droplets 18 are ejected, is positioned on the surface of the substrate 30 and forms an upper wall of the ink chamber 15. A ring-shaped heater 22, which is adjacent to and surrounds the nozzle 21, is formed in the nozzle plate 20. An electric wire (not shown) for applying an electric current is connected to the heater 22.
In the above structure, if a pulse current is applied to the ring-shaped heater 22 in a stage in which the ink chamber 15 is filled with ink supplied from the manifold 26 through the ink channel 13, ink under the heater 22 boils by heat generated by the heater 22, and bubbles are generated in the ink. As a result, pressure is applied to the ink within the ink chamber 15, and ink in the vicinity of the nozzle 21 is ejected as the ink droplet 18 through the nozzle 21. Subsequently, ink flows into the ink chamber 15 through the ink channel 13, thereby refilling the ink chamber 15 with ink.
In this second conventional ink-jet printhead, only a portion of the substrate 30 is etched to form the ink chamber 15. Thus, a size of the ink chamber 15 can be reduced. In addition, because the printhead is manufactured by a batch process without a bonding process, a process of manufacturing the ink-jet printhead is simplified.
In this configuration, however, since the ink channel 13 is positioned in a same line as the nozzle 21, ink flows back toward the ink channel 13 when bubbles are generated, thereby lowering an ejection property. In addition, since the substrate 30 exposed by the nozzle 21 is etched to form the ink chamber 15, the size of the ink chamber can be reduced, but the ink chamber 15 cannot be formed with various different shapes. Thus, it is difficult to form an ink chamber having an optimum shape.
FIG. 3 illustrates a cross-sectional view of the structure of still another conventional ink-jet printhead. Referring to FIG. 3, the ink-jet printhead includes a nozzle plate 50 having a nozzle 51, an insulating layer 60 having an ink chamber 61 and an ink channel 62, and a silicon substrate 70 having a manifold 55 for supplying ink to the ink chamber 61. The nozzle plate 50, the insulating layer 60, and the silicon substrate 70 are sequentially stacked.
In this third conventional ink-jet printhead, since the ink chamber 61 is formed using the insulating layer 60 stacked on the substrate 70, the ink chamber 61 may have a variety of shapes, and a backflow of ink may be reduced.
When manufacturing this third conventional ink-jet printhead, however, a method of depositing the thick insulating layer 60 on the silicon substrate 70, etching the insulating layer 60, and forming the ink chamber 61 is generally used. This method has the following problems. First, it is difficult to stack a thick insulating layer on a substrate using existing semiconductor processes. Second, it is difficult to etch a thick insulating layer. Thus, there is a limitation on the depth of the ink chamber. As shown in FIG. 3, the ink chamber 61 and the nozzle 51 have a combined height of only about 6 μm. With such a shallow ink chamber, however, it is virtually impossible for an ink-jet printhead to have a relatively large drop size.